Well, this turned out to be a completely different question than the one I started writing!

Originally I was wondering how to make a version of \textit (and a parallel version of \textsl) that automatically tracks the nesting level and toggles on/off based on the oddness/evenness of the nesting depth. \emph of course does this, but it isn't guaranteed to render in italics, and there doesn't seem to be a corresponding slant version of \emph for slant.

And then I discovered the slemph package, which provides exactly what I want. Sometimes, while formulating a question, one thinks of better search terms/phrases and is better able to find the answer!

Anyway, I figured that a picture would be the best way to ask my question (originally), so I started out by making this drawing, which describes fictional macros \RM, \IT, \SL, and \BF which behave well together like \textit, \textsl, \textbf, etc.:

And then I made this, which demonstrates the inner workings of the decision-making that I was hoping to hack together:

But again, it turns out that \textitswitch and \textslswitch of package slemph already do exactly what I want, and I basically wasted my time making the diagrams. But I did learn some new things. :-)

So, as long as I have these diagrams (and the accompanying LaTeX source), I'm wondering if there is a preferred way to submit things to package authors for their consideration. Is it acceptable to just e-mail them? Or is there a more formal gateway through CTAN? This particular package hasn't been updated in 13 years.

I would definitely find a diagram like this helpful in the documentation for the package. I actually came across the package halfway through my investigation, but brushed it aside carelessly because I didn't realize from the description that it actually did what I wanted! A picture like this would have led me to see it immediately.

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